1. Field of the Invention
The present invention relates to a stencil printer of the type including a plurality of print drums and capable of completing multicolor printing in a single flow.
2. Description of the Background Art
A digital, thermosensitive stencil printer is extensively used as a simple, convenient printer and loaded with a stencil made up of a thermoplastic resin film and a porous support adhered together. The stencil printer includes a thermal head having a number of heat generating elements arranged thereon and conveying means, including a platen roller, for conveying the stencil held in contact with the thermal head. The heat generating elements of the thermal head are selectively energized by pulse current in order to selectively perforate, or cut, the thermoplastic resin film of the stencil with heat in accordance with image data. The perforated part of the stencil, i.e., a master is cut off and then wrapped round a porous, hollow print drum. Subsequently, a paper sheet or similar recording medium is pressed against the outer periphery of the print drum with the result that ink is transferred to the paper sheet via the porous portion of the print drum and the perforations of the master, forming an image on the paper sheet.
Today, multicolor printing for producing multicolor prints with the principle of stencil printing stated above is spreading. Japanese patent laid-open publication No. 10-297074, for example, discloses a stencil printer of the type including a plurality of print drums arranged side by side and each storing ink of a particular color. When the print drums are rotated in synchronism with each other by a single drive means, pressing means, corresponding one-to-one to the print drums, sequentially press a sheet against the print drums in order to sequentially transfer the ink of different colors to the sheet one above the other. As a result, a multicolor print is produced by a single flow.
Further, duplex printing for printing images on both sides of a sheet is extensively used for the purpose of reducing sheet consumption and a document storing space. Japanese patent laid-open publication No. 2003-200645, for example, proposes a stencil printer operable in a duplex print mode by using a master in which a first and a second image are cut, or perforated, side by side in the direction of rotation of a print drum. In operation, one of the first and second images is printed on one side of a first sheet fed from a sheet feeding section, and then the first sheet is conveyed to an auxiliary tray. Subsequently, the above image is printed on one surface of a second sheet also fed from the sheet feeding section, and then the second sheet is conveyed to the auxiliary tray. At the same time, the first sheet is again fed from the auxiliary tray in order to have the other image printed on the other surface thereof and is then driven out to a print tray. Such a procedure is repeated to produce duplex prints by a single flow.
Although the prior art stencil printers taught in the documents stated above can execute either one of multicolor printing and duplex printing in a single flow each, they cannot execute duplex multicolor in a single flow.